The present invention relates to Gifford McMahon (G-M) type multi-port pulse tube refrigerators. G-M type pulse tubes consist of a compressor, a valve mechanism, and an expander. The present invention improves on a previous rotary valve disc and valve seat mechanisms. The improvement lies in replacing the face seal ports for flow to and from the regenerator with a rotary spool valve having radial clearance, while retaining the face seal ports for flow to and from the pulse tubes.
It has been found that best performance at 4 K has been obtained with a pulse tube as shown in FIG. 9 of Gao, U.S. Pat. No. 6,256,998. This design has two valves controlling flow to the regenerator, and four valves controlling flow to the warm ends of the pulse tubes, which open and close in the sequence shown in FIG. 11 of U.S. Pat. No. 6,256,998. The single stage version of this pulse tube has four valves, two to the regenerator and two to the pulse tube, thus this control is commonly referred to as four-valve control. The main problem of multi-ported rotary disc valves is that the diameter of the disc is significantly increased, relative to the two ported valves that are commonly used in standard G-M refrigerators to control flow to and from the regenerator, to accommodate the valve ports that control flow to and from one or two pulse tubes.
Various solutions have been proposed to minimize the diameter of a rotary disc valve but the high to low pressure difference increases the sealing force substantially and thus requires a motor with larger torque to turn it. The sealing force of a larger diameter valve can be reduced by transferring some of the force to an axial bearing as described in Lobb, U.S. Pat. No. 4,987,743, and Heron, U.S. Pat. No. 6,694,749.
While these methods to reduce the sealing force, and thus the torque required to turn the valve, are effective, the wear dust from the plastic type material that is typically used for the valve disc against a hard valve seat generally collects in the orifices that control flow to and from the pulse tubes and changes the cooling performance over time.
The problems of reducing the torque required to turn the valve, eliminating wear dust, and extending the life of the valve, have been addressed in pending patent application U.S. Ser. No. 60/551,154, entitled “Wearless Valve”. This solution to these problems is based on supporting the rotating valve disc on a bearing and maintaining a small clearance between the valve disc and the valve face. This works well when the proper clearances are established. The small ports that control flow to and from the pulse tubes are very sensitive to leakage while the ports that control flow to and from the regenerator are less critical.
Yaron, U.S. Pat. No. 5,901,737 describes a rotating spool valve for a G-M type refrigerator that uses gas bearings to center the spool so that a small clearance can be maintained without contact. Sarcia, U.S. Pat. No. 4,333,755 describes a spool valve that shuttles back and forth to switch flow to the regenerator in a G-M type refrigerator
It is an object of the present invention to provide an alternate solution to these problems in a simpler construction by using a rotary spool valve.